feat(admin): add initial admin dashboard structure

This commit introduces the foundational structure for the new admin dashboard.

- Utilizes @nuxt/ui to build the dashboard layout, including a collapsible sidebar and navigation.
- Adds initial pages for the dashboard, news, events, and hall of fame management.
- Implements a composable `useDashboardSidebarLinks` for managing sidebar navigation.
- Refactors the default layout by integrating the header and footer directly.
- Swaps the primary and secondary theme colors across the application.

app/layouts/default.vue

@@ -1,8 +1,63 @@
 <template>
   <div>
-    <AppHeader />
+    <!-- 导航栏 -->
+    <header class="bg-white shadow-md sticky top-0 z-50">
+      <div class="max-w-6xl mx-auto px-4 py-3 flex justify-between items-center">
+        <div>
+          <img class="inline w-16" src="/Logo.svg" alt="YPHS Alumni">
+          <h1 class="inline text-xl font-bold text-gray-900">
+            <a href="/" class="ml-4 hover:text-primary">永平中学校友会</a>
+          </h1>
+        </div>
+        <nav class="space-x-6 hidden md:flex items-center">
+          <a href="#news" class="hover:text-primary">新闻</a>
+          <a href="#events" class="hover:text-primary">活动</a>
+          <a href="#donate" class="hover:text-primary">捐赠（未开放）</a>
+          <a href="#about" class="hover:text-primary">关于</a>
+          <a href="/join-us"
+            class="inline-flex items-center gap-2 bg-primary text-white px-4 py-2 rounded-xl shadow hover:opacity-90">
+            加入
+            <Icon name="mdi:account-plus" class="w-5 h-5" />
+          </a>
+
+        </nav>
+      </div>
+    </header>
+
     <slot />
-    <AppFooter />
+
+    <!-- 页脚 -->
+    <footer class="bg-gray-900 text-gray-300 py-6">
+      <div class="max-w-6xl mx-auto px-4 flex flex-col md:flex-row justify-between items-center">
+        <!-- 左侧版权信息 -->
+        <div class="text-center md:text-left">
+          <p>© 2025 永平中学校友会. 保留所有权利.</p>
+        </div>
+
+        <div class="">
+          <p class="mt-1">
+            Powered by:
+            <a href="https://tootaio.com" target="_blank" class="font-semibold hover:underline" style="color: #e24545;">
+              Tootaio Studio
+            </a>
+            <span class="mt-1 text-sm text-gray-400">2018 级毕业学长（麦祖奕）</span>
+          </p>
+        </div>
+
+        <!-- 右侧社交链接 -->
+        <div class="flex space-x-4 mt-3 md:mt-0">
+          <a href="#">
+            <Icon name="mdi-facebook" />
+          </a>
+          <a href="#">
+            <Icon name="mdi-instagram" />
+          </a>
+          <a href="#">
+            <Icon name="mdi-gmail" />
+          </a>
+        </div>
+      </div>
+    </footer>
   </div>
 </template>
 
@@ -10,6 +65,4 @@
 
 </script>
 
-<style>
-
-</style>
+<style></style>